All beds are for people to sleep on.
A riverbed is a bed.
Therefore a riverbed is for people to sleep on.
The conclusion of this syllogism is valid, as it follows the presented premises. However, this argument is not true, due to the untrue premises. As a result, this argument is not sound.
A: Middle Term = Beds
B: Predicate Term = For people to sleep on
C: Subject Term = A riverbed
This syllogism follows the proper form of a categorical syllogism: All (A) are (B). (C) is an (A). Therefore (C) is a (B).
Though at first glance the first premise may seem true, but due to its lack of clarity and specificity, it is not so. Without defining the word “bed”, the word can refer to any kind of bed, such as “roadbed,” “hotbed”, or “riverbed,” like in the premises. These examples are all some sort of base or foundation in which other materials or substances are placed upon, therefore all fall under the definition of beds. This disapproves that “All beds are for people to sleep on.” Therefore, the first premises is false. In order for this premise to be true, additional information is necessary. For example, if “that are designed for humans” was added on, it would now read: “All beds that are designed for humans are for people to sleep on.” “Roadbed,” “hotbed”, or “riverbed,” would no longer fall under this category of beds.
Though the conclusion is not true, one could still attempt to sleep upon a riverbed. Just because it isn’t for people to sleep on, doesn’t mean it can’t be.